Image-based tracking of eye movement or position is known to be used for several applications such as surgery and diagnostics, one example being a retinal diagnostic/surgical device. However, conventional eye tracking techniques suffer from several problems. One problem is the image quality provided by the system, e.g. the signal-to-noise ratio SNR. If the SNR is low, then the image processing techniques used for eye tracking are not as accurate as they could be. Moreover, there are problems which are due to the specific instrumentational configuration.
One such example is retinal video tracking for a Optical Coherence Tomography (OCT) device for measuring thickness and structure of the retinal layers, but other specific fields such as devices for surgery, diagnosis or monitoring of the eye can be mentioned here as well.
In case of an OCT system, the measurement beam of the OCT interferes with the fundus imaging due to fact that the illumination spectrum of the beam is close to the imaging spectrum (near IR). The effects of the OCT beam can be described as having two components:                Saturations of the image on small areas where the beam hits the retinal surface        Low frequency illumination changes that are caused by beam light diffusion at the retinal surface and beam light reflection from retinal surface.        
Additionally image is corrupted by acquisition noise and by illumination distortions caused by the pupil size and alignment changes during the procedure.
can be applied to any device in which either a measurement scanning beam or surgical laser beam effects the retinal image used for tracking or alignment.
It is therefore an object of the present invention to provide a method and apparatus which is capable to enhance the performance of a conventional eye tracking system.